1. Field of the Invention
The present invention concerns an antistatic surface coating checking device intended for ensuring that a structure made up of a metal frame including both metal panels and insulating panels coated with a layer of conducting material, the surface of these panels being entirely finished with an insulating paint, is capable of withstanding the action of the electrostatic phenomena to which it is subjected with no adverse effect. To be more precise, this device makes it possible to verity that the panels are indeed electrically grounded to the metal frame with a view to checking out the effectiveness of the antistatic protection provided by the conducting layer covering the structure insulating elements.
The antistatic protective measures, particularly those employed in the aerospace industry, can be broken down into two categories:
those applied to structural elements not requiring radioelectric transparency properties (example: access doors, wing sections, tip ends, etc.);
those applied to the dielectric walls protecting navigation, communication or detection equipment and consequently calling for radioelectric transparency properties (example: radome, aerial fairings, missile caps, etc.).
In the first case, the antistatic deposits applied can have very low surface resistance values. In the second case, the deposits made must provide high and perfectly controlled surface resistances in order to afford a compromise between the continual flow of static charges and the necessary radio-transparency properties. This compromise gives rise, in the majority of applications, to surface resistances lying between 10.sub.5 and 10.sup.8 ohms per square.
In virtually all aerospace applications (airplanes, helicopters, missiles), the antistatic treatments are themselves followed by the application of a finishing paint (for the purposes of aesthetics as regards commercial aircraft, optical detection for the experimental missiles, particle impact resistance, corrosion immunity, thermal balance, etc.). This finishing paint is an insulator and rules out, on the face of it, any process for measuring or checking the subjacent electrostatic protection using electrodes in electrical contact (megohmmeter with plane or circular electrodes).
2. Description of the Prior Art
French Pat. No. 1 333 449 filed Sept. 12, 1962 discloses a surface resistivimeter having central and annular coaxial electrodes made of conducting rubber. This resistivimeter permits the measurement of the resistance of bare metallic surfaces; it cannot measure the resistances of surfaces coated with an insulating layer, nor it can test electrical continuity of a structure having a ground terminal.